The invention relates to ceramic matrix nanocomposites containing nanotube materials.
Ceramics are used in applications requiring strength, hardness, light weight and resistance to abrasion, erosion and corrosion, at both ambient and elevated temperatures. Examples of high temperature applications include structural parts for heat engines, including automobile engines and gas turbines; tools and dies, especially cutting tools for heat resistant alloys used in chip manufacture; and wear and/or friction surfaces. However, traditional ceramic materials are characteristically brittle, and this brittleness limits their use. Some reduction of brittleness has been obtained with fiber-reinforced ceramic matrix composites. Examples of these composites are whisker-reinforced ceramic carbides which have been used as cutting tools. Nevertheless, there continues to be a need for materials which combine the desirable properties of ceramics with improved fracture toughness.
It has been unexpectedly discovered that ceramic nanocomposites comprising nanotube fillers and nanocrystalline ceramic materials display improved fracture toughness over monolithic ceramic materials. In particular, carbon nanotubes exhibit surprising stability as fillers in nanocrystalline ceramic oxide matrixes and produce significant improvements in fracture toughness in the final composite material.
In one aspect, then, the present invention relates to a ceramic matrix nanocomposite comprising a nanotube filler comprising at least one nanotube material and a ceramic matrix comprising a nanocrystalline ceramic oxide. The nanotube material may be a carbon nanotube material, specifically a single walled, multi-walled, or surface modified carbon nanotube material. The nanocrystalline ceramic material may be a ceramic metal oxide. The metal of the ceramic metal oxide may be aluminum, titanium, zirconium, magnesium, yttrium, or cerium. In particular, the metal may be aluminum, titanium or zirconium. Specifically, the metal oxide may be alumina. The amount of nanotube filler in the nanocomposite is about 0.5 to 50 parts by volume; the amount of ceramic matrix is about 50 to 99.5 parts by volume. In particular, the amount of nanotube filler may be 1 to 20 parts by volume, and the amount of ceramic matrix about 80 to 99 parts by volume.
In another aspect, the invention relates to a method for producing ceramic articles having improved fracture toughness comprising combining a nanotube filler comprising a nanotube material and a ceramic matrix comprising at least one nanocrystalline ceramic oxide; forming an article therefrom; and sintering the article under elevated pressure at elevated temperature. The nanotube material may be a carbon nanotube material, specifically a single walled, multi-walled, or surface modified carbon nanotube material. The nanocrystalline ceramic material may be a ceramic metal oxide. The metal of the ceramic metal oxide may be aluminum, titanium, zirconium, magnesium, yttrium, or cerium. In particular, the metal may be aluminum, titanium or zirconium. Specifically, the metal oxide may be alumina. The amount of nanotube filler in the nanocomposite is about 0.5 to 50 parts by volume; the amount of ceramic matrix is about 50 to 99.5 parts by volume. In particular, the amount of nanotube filler may be 1 to 20 parts by volume, and the amount of ceramic matrix about 80 to 99 parts by volume.
In yet another aspect, the invention relates to ceramic articles comprising a ceramic matrix nanocomposite as described above. The article may be a wear surface, a bearing surface, a cutting tool, or a structural ceramic article.
In yet another aspect, the invention relates to a ceramic matrix nanocomposite comprising a nanotube filler comprising at least one nanotube material and a ceramic matrix comprising a nanocrystalline ceramic material. Where the nanotube filler is a carbon nanotube material, the nanocrystalline ceramic material may not be silicon carbide. The nanocrystalline ceramic material may be an oxide, carbide, nitride, oxycarbide, oxynitride, carbonitride, oxycarbonitride, carbonate, phosphate or a mixture thereof. In particular, the nanocrystalline ceramic material may be a metal oxide, a metal carbide, a metal nitride, a metal oxycarbide, a metal oxynitride, a metal carbonitride or a mixture of the above. The amount of nanotube filler in the ceramic matrix nanocomposite is about 0.5 to 50 parts by volume; the amount of nanocrystalline ceramic material is about 50 to 99.5 parts by volume. Specifically, the amount of nanotube filler may be 1 to 20 parts by volume; the amount of nanocrystalline ceramic material may be about 80 to 99 parts by volume. In particular, the ceramic matrix nanocomposite may comprise about 1 to 20 parts by volume of a multi-walled carbon nanotube material, and about 80 to 99 parts by volume of a nanophase alumina.